Machinery powered by electric motors or internal combustion engines (typically referred to as "prime movers") often use gears, shafts and the like to form a drive train providing power used to perform an end-use function. Automobiles, metal cutting and shaping machines, toggle-type presses and construction and earth-moving machines are but a few examples of such machinery.
As more specific examples, such machinery drive trains uses gears and shafts in speed reducers and right angle drives to reduce speed (from that of the motor or engine output shaft) and increase torque and/or to change the direction of power flow. Shafts interconnect "stages" of gearing or connect a final gearing stage to an output device such as automobile wheels, press head or, in the case of an earth-moving machine known as a walking dragline, to a "walk leg" drive.
In such machines, the drive train components (gears, shafts and the like) range in size from a few pounds to several thousand pounds. Clearly, small drive train components can be readily lifted, manually placed and positioned by one or two maintenance workers. Equally clear is the fact that assembly and maintenance personnel working with very large drive train components usually need auxiliary lifting equipment, a crane or the like, to help them lift and place such components.
Another characteristic of certain types of machines, e.g., toggle presses and walking draglines, is that certain machine functions tend to load (and wear) certain drive train components unevenly. For example, the drive train of a toggle press (especially that portion driving the toggle press head mechanism) is most heavily loaded over only that fraction of a revolution relating to the final, piece-forming part of the press stroke. In a walking dragline, the walk leg drive is most heavily loaded only during that part of a revolution during which the dragline is being lifted to take a "step."
To keep the machine functioning efficiently and in condition to satisfactory perform its task, worn parts need to be replaced. However, with larger machines, maintenance and parts replacement can be an imposing challenge, especially if the parts are large and unwieldly. Nowhere is this more true than in large mobile machines such as earth-moving and earth-excavating machinery.
Such machinery is available in a wide variety of types ranging from the familiar rubber-tire mounted and crawler-mounted to the less-common dragline. A dragline is often used for removing top soil and "overburden" to expose a valuable mineral, e.g., coal, beneath but near the earth's surface.
Draglines are equipped with an angularly-extending boom from which is suspended a "bucket" having an open mouth and digging teeth, both toward the main portion of the machine. Overburden is removed by placing the bucket on the ground at a point distant from the machine and pulling it toward the machine, filling the bucket in the process. Once filled, the machine pivots about a central axis and the bucket emptied at a spoil pile somewhat away from the area being excavated.
Smaller draglines are crawler mounted (much like a military tank) and capable of movement in the same way albiet at much slower speeds. However, as draglines (and their digging buckets) increased in size, crawler mounting was found to be impractical and in the early 1900's, the "walking" dragline was developed. The walking dragline is so named because it takes short "steps" and uses a "walk leg" mechanism (which resembles a human leg) to do so. A difference is that in a walking dragline, both legs step simultaneously.
To give some perspective to the following discussion, a large walking dragline--made by Harnischfeger Industries of Milwaukee, Wisconsin, and incorporating the invention--has a main housing portion (including the machinery deck, operator's cab and the like) which is about 105 feet long, about 80 feet wide, about 40 feet high and weighs about nine million pounds. The boom extends about 300 feet and the capacity of the digging bucket is about 80 cubic yards. The walk legs of such dragline take steps about seven feet in length.
At least because of its size, weight and complexity, several problems attend draglines of earlier configuration. One is that such machines are usually used in remote sites and replacement parts are difficult to deliver and, because of their size and weight, even more difficult to install.
Wear cannot be avoided in any device having relatively moving parts but the efforts of earlier designers of draglines and their drive trains have not been entirely successful in reducing maintenance time and "downtime" of a machine representing a very substantial capital investment. Earlier machine drive trains are sometimes characterized by certain disadvantages. One is that individual drive train components are not self supporting. When being assembled or worked upon for maintenance purposes, one or more of the components must be lifted and handled by auxiliary lifting equipment.
Another, related disadvantage is that such components cannot be readily re-positioned with respect to one another without the use of such lifting equipment. Still another disadvantage is that re-positioning is manual rather than under power of the prime-mover. And the larger the components, the more pronounced are the disadvantages.
An improved drive train apparatus permitting drive component disconnection and re-positioning under power of the prime mover and permitting certain maintenance work without using auxiliary lifting equipment would be an importance advance in the art.